Medical professionals presently locate a blood vessel by palpitation or by blocking circulation in the vessel downstream from the needle insertion point, then looking for the bulging vessel. In many cases this procedure is unsuccessful in locating the vessel. Medical professionals may repeatedly stick the patient until they locate the vessel. Often, even when the vessel is successfully located, the needle penetrates too deeply, penetrating both walls of the vessel and striking a nerve. This problem is particularly acute when the patient is a small child. Or, a located vessel has a tendency to rotate or roll away from the needle as the medical professional attempts to insert it, further complicating the procedure.